1. Field of the Invention
The present invention relates to a motor driven antenna for vehicles, such as automobiles, etc. which prevents vibrations originating from the motor mechanism thereof from being transmitted to the vehicle body.
2. Prior Art
Generally, conventional motor driven antennas of this type have an extendible antenna element in a stick form stored in an antenna housing tube. The top end portion of the antenna housing tube has an inlet/outlet opening for the antenna element and is fixed to a fitting hole on the body of the vehicle. A motor mechanism for extending and retracting the antenna element is mounted on the base of the antenna housing tube. A motor mechanism casing and the antenna housing tube are usually connected to each other by directly fitting the base end of the antenna housing tube to a housing tube holding portion of the motor mechanism casing, and then fixing them to each other with fastening means such as screws, etc.
The conventional motor driven antennas described above, however, have problems such as when the motor mechanism is actuated to extend and retract the antenna, vibrations caused by rotation of the motor as well as rotation of a rotary drum in the motor mechanism, vibrations caused by sliding of the antenna driving wire and vibrations which occur due to the impact caused during extension and retraction of the antenna element, etc. are transmitted to the vehicle body through the antenna housing tube. As a result, very loud noises are generated due to the resonance phenomena caused by the vibrations. Such noise is extremely unpleasant to the user and an improvement to reduce the noise has been strongly desired. In order to prevent such noise, several devices have been devised.
In one such means the end portion of the antenna housing tube is fitted to the vehicle body using a vibration absorbing member provided between them. However, since the vibration absorbing member is provided where the antenna is firmly fixed to the vehicle body, it is difficult to allow the vibration absorbing member to be sufficiently thick so that it can function properly. Accordingly, the vibrations cannot be sufficiently absorbed.
Another device designed to reduce vibration of the motor mechanism uses a vibration absorbing member placed between the motor mechanism and a mounting bracket. This device, however, is defective because although vibration of the motor mechanism is reduced, vibrations caused due to sliding of the wire, etc. cannot be sufficiently absorbed, and the remaining constituent vibration is transmitted to the vehicle body through the antenna housing tube. Thus, it is impossible to obtain advantageous results.
In another device vibration of the motor mechanism is prevented from being transmitted to the vehicle body by connecting the middle portion of the antenna housing tube with rubber tubes, etc. Although the desired result can be obtained to a certain extent with this device since the middle part of the antenna housing tube is connected with rubber tubes, etc., which are elastic members, the antenna housing tube cannot be held securely, and lateral shake of "&lt;" shape occurs in the antenna housing tube due to vibration of the vehicle body, etc.